The present invention relates to a dried singulated cellulose pulp fiber product as well as a process for producing dried singulated cellulose pulp fibers, and more particularly, a process for producing dried singulated cellulose pulp fibers using a jet drier.
Dried singulated cellulose pulp fibers are desirable for many products from absorbent personal articles to a strengthener in concrete. Currently, in the most common process of making singulated fibers, a roll of conventional pulp fibers is hammermilled into singulated fibers. This process is energy and time intensive, requiring many steps and pieces of processing equipment. Each piece of processing equipment requires a significant capital expenditure and occupies valuable factory floor space. Further, the current hammermilling process often produces fibers with undesirable physical properties, such as low kink, curl, and twist.
This dry singulated pulp will also contain knots of fiber, sometimes referred to as nits or nodules. Knots are fiber clumps that remain strongly adhered to one another as can be seen by placing a small portion of pulp into a clear beaker of water and stirring the water to mix the fibers. Most of the fiber will mix into the water as singular fibers, however there will be fiber clumps that are readily visible. The fiber clumps or knots are undesirable by-products of the hammermilling process. The amount of knots in a pulp that has been hammermilled can be quantified by using a screening system with acoustical energy used as the means to classify the fiber into sizes of knots, accepts and fines. It is desirable to have low knots and fines and high accepts where the accepts are the singulated fibers.
Canadian Patent No. 993618 (Estes, 1976) describes a process for producing a low density fluff pad or batt from individual fibers that have significant kink and interlocking to provide improved batt strength and higher bulk. In accordance with the process, wet pulp is separated into individual fibers during the drying stage. The process uses fluid jet drying equipment that employ air-jets or steam-jets for separating the fibers. The fibers are laid on a perforated screen upon exiting from the jet drier. The fibers produced by the process of the Canadian patent, however, have a very high knot content, which as stated above is an undesirable characteristic.
This invention provides a dried singulated cellulose pulp fiber product as well as a method for forming singulated and dried fibers that have a relatively low knot content. In accordance with the process, wet pulp, steam, and air are introduced into a jet drier. The pulp is dried in the jet drier to form singulated pulp fibers. The pulp is removed from the jet drier and separated from the air. The process may be used on several types of feed pulp and on treated feed pulp. The product formed by the process has advantageous properties such as a low knot count, a low fines count, as well as improved kink, curl and twist.
A drying system for the processing of pulp into singulated and dried fibers includes a jet drier, a pulp supply station, an air supply station, an outlet flow conduit and a fiber separation station. The jet drier has a jet conduit, a manifold for air intake into the jet conduit, a steam injection port, a pulp intake for delivery of pulp into the jet conduit, and a fiber outlet for removal of singulated and dried fibers, outlet air and fines from the jet conduit. The pulp supply station is coupled to the pulp intake for supplying a feed pulp to the pulp intake. The air supply station is coupled to the manifold for delivering air to the manifold. Steam is supplied under pressure to the steam injection port. The outlet flow conduit is coupled to the fiber outlet for the transport of the fibers, outlet air and fines from the jet conduit. The fiber separation station is coupled to the outlet flow conduit for separating the fibers from the outlet air.
The present invention thus provides a dried singulated cellulose pulp fiber product as well as a method that enable forming singulated and dried fibers having a low knot content. The process may take wet pulp directly from a pulp mill and produce a singulated product from never-dried or once-dried pulp. Using steam in the process forms fibers with greater kink, curl, and twist than hammermilled fibers. A further advantage of using steam is the ability to produce fibers having a low knot and fines content. The addition of steam during the jet drying process results in a more stable outlet temperature. The fiber mat produced also appears to be more uniform. Product moisture, however, preferably is still within acceptable range of less than 6% to 10%. In addition, a measurable reduction in sonic knots was achieved relative to conventional untreated fiber dried using the jet drier alone.